The principle of sleeving the main tube of a riser in offshore drilling is known from the prior art. However, prior art devices are based on the principle of a rigid connection between the sleeving conduit elements providing transmission of a longitudinal force and tightness between the inside and the outside of the sleeving.
Such connections may be produced in the same manner as those ordinarily used for well tubing with a threaded assembly which is fairly time-consuming and difficult to effect, and whose reliability of tightness and mechanical strength over a given time period may be questionable after several assembly and disassembly operations. Specially designed connectors of the riser connector type are difficult to design in view of the small space available and would considerably increase the weight and cost of sleeving.
Because of the principle upon which prior sleevings have been developed, the prior sleeving systems require the use of a sliding seal inserted into the sleeving in order to compensate for the differential longitudinal deformations of the sleeving conduit and the tube under the effect of variations in traction, pressure and temperature. This sliding seal, since it requires a long travel path, may be several meters in length and is difficult to use since the seal is subjected to substantial pressure differentials and especially since the seal would be located at a lower part of the sleeving conduit.